Tractors and other forms of off-highway implements typically include a driven transmission assembly which is shiftable from a neutral condition to any of plurality of drive conditions to provide the operator with a broad range of operating conditions. In some offhighway implements, the transmission assembly includes a speed transmission and a range transmission arranged in combination with one another. The speed transmission typically includes a combination of gear meshes which define different power paths through the transmission. Synchronizers are commonly used between the different gear meshes to facilitate conditioning of the transmission during a shift from one power path to another power path. Similarly, the range transmission includes a combination of gear meshes which define different power paths through the range transmission. It is not unusual for the speed and range transmission combination to provide the operator with up to 16 different drive conditions in which the implement can be operated.
The speed transmission is typically connected to the engine of the implement as through a clutch assembly. A typical clutch assembly includes a manually actuated clutch pedal which is biased into a preset position. As is conventional, depression of the clutch pedal by a predetermined amount effectively disconnects the driven transmission assembly from the engine and allows either the speed transmission or range transmission to be shifted from either a neutral condition to any of several different other conditions in which the operator desires to operate the implement.
Each transmission of the driven transmission assembly includes a shift mechanism for conditioning the respective transmission. As is well known, an elongated shift lever is connected to and conditions each respective transmission as through a shifting assembly. The shift lever is movable from a neutral position which corresponds to the neutral condition of the tractor or implement into the desired drive condition. The shifting assembly is responsive to the movements of the shift lever and is connected to the respective transmission.
Upon leaving the cab region of the implement, an operator commonly places the shift mechanism in a neutral position. Because of the confined space restraints in the cab region of the tractor, however, it is not unusual for an operator to inadvertently move the shift lever from the neutral condition upon entering or leaving the cab region. The problems with having the shift mechanism mistakably condition the driven transmission assembly in other than a neutral condition are well known in the art.
Various devices have been proposed and used for preventing operation of the implement until the transmission assembly is in a neutral condition. One well known device for effecting these ends includes a series of electric ball switches which are mounted within each transmission. These heretofore known switch devices are conventionally used to detect the linear position of the transmission shift rail relative to a neutral condition.
These heretofore known electric switch devices are relatively sensitive and have been known to fail after very short use. Thus, considerable time and effort is spent repairing and/or replacing the switches in the transmissions. Replacement of the switches often requires access to the transmission interior to effect sensitive adjustments thereby allowing proper operation of the switch. As will be appreciated, repair, replacement, and adjustment of the electrical switches results in "down time" for the tractor. Thus, the benefits achievable through the use of such devices is often offset by the time spent on repairing and/or replacing such devices.
Thus, there is a need and a desire for a transmission assembly shifting mechanism which includes a neutral lock system that is reliable in preventing movement of the transmission shifting mechanism from a neutral condition until purposefully desired by the operator.